1. Field of the Invention
The present invention relates to a film formation apparatus and a film formation method employed for film formation of a film formable material (herein after, referred to as a deposition material) by deposition. Additionally, the invention relates to a cleaning method for removing a deposition material adhering to the inner wall or the like by the deposition. Particularly, the invention is an efficient technique in the case an organic material is used as the deposition material.
2. Related Art
In recent years, investigations of light emitting apparatuses comprising EL elements as self-luminous type elements have been enthusiastically carried out and specially, light emitting apparatuses using organic materials as EL materials have drawn attention. Such a light emitting apparatus is called as an organic EL display (OELD) or an organic light emitting diode (OLED).
The EL element comprises a layer (herein after referred to as an EL layer) containing an organic compound capable of emitting electroluminescence by electric field application, an anode, and a cathode. The luminescence in the organic compound includes light emission (fluorescence) at the time of returning to the normal state from the singlet state and light emission (phosphorescence) at the time of returning to the normal state from triplet state and a light emitting apparatus to be manufactured by the film formation apparatus and the film formation method of the invention is applicable for cases using both fluorescence and phosphorescence.
The light emitting apparatus has a characteristic that it has no problem in the visible angle because it is self-luminous type, not a liquid crystal display apparatus. That is, as a display to be employed outdoors, the apparatus is more suitable than a liquid crystal display and application in various manners has been proposed.
The EL element has a structure in which the EL layer is sandwiched between a pair of electrodes and the EL layer generally has a layered structure. A typical example is a layered structure of a hole transporting layer/a light emitting layer/an electron transporting layer proposed by Tang, Eastman Kodak Co. The structure has a remarkably high light emitting efficiency and almost all of light emitting apparatuses which have been presently investigated and developed employ the structure.
Further, structures of a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer formed successively on an anode and of a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer/an electron injecting layer may be employed. A fluorescent coloring material or the like may be doped in the light emitting layers. Further, these layers may be formed by using materials all with low molecular weights or using materials all with high molecular weights.
Incidentally, in the specification, all layers to be formed in a cathode and an anode are generically named as an EL layer. Accordingly, the above-mentioned hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer, electron injecting layer are all included in the EL layer.
Also, in the specification, the light emitting element composed of a cathode, an EL layer, and an anode is called as an EL element and there are two types of the EL element: one is a simple matrix type in which the EL layer is formed between two kinds of stripe-like electrodes formed at right angles to each other and the other is an active matrix type in which the EL layer is formed between pixel electrodes connected to TFT and arranged in a matrix and a counter electrode.
The most important problem of the EL element on practical application is that the life of the element is insufficient. The deterioration of the element appears in a way that a non-light emitting region (a dark spot) is widened as the light emission is carried out for a long time and as a cause of the deterioration, the EL layer deterioration becomes an issue.
The EL materials forming the EL layer are deteriorated by impurities such as oxygen, water and the like. Further, it may be also possible that the deterioration of the EL layer is affected by contamination of the EL materials with other impurities.
Further, the EL materials are divided broadly into low molecular weight (monomer-type) materials and high molecular weight (polymer-type) materials and among them, the low molecular weight materials are mainly formed into films by deposition.
In the case of film formation by a conventional deposition method, a deposition material is used as it is, but the deposition material for the deposition, is supposed to be contaminated with impurities. That is, oxygen, water, and other impurities, which are one of the causes of deterioration of the EL element, are probably mixed therein.
Further, although the purity can be increased by previously refining the deposition material, there is probability that impurities are mixed by the time when evaporation is carried out.
EL materials are extremely susceptible to deterioration and easily oxidized and deteriorated in the presence of oxygen or water. For that, a photolithographic process cannot be carried out after film formation and in order to form a pattern, the film has to be separated using a mask having openings (herein after referred to as a deposition mask) simultaneously with film formation. Accordingly, almost all of the sublimated organic EL materials adhere to a deposition mask or a deposition-preventing shield (a protective plate for preventing adhesion of the deposition materials to the inner walls of a film formation chamber) in the film formation chamber.
In order to remove the organic EL materials adhering to the deposition mask or the deposition preventing shield, it is required to open the film formation chamber to the atmospheric air once, take the deposition mask or the deposition preventing shield outside and then return it again to the film formation chamber after washing it. However, water or oxygen adsorbed in the deposition mask or the deposition preventing shield exposed to the atmospheric air may be probable to be isolated and taken in the film at the time of film formation using the organic EL materials and thus it is apprehended that adsorbed water or oxygen may be a factor of promoting deterioration of the organic EL materials.
The invention is achieved in consideration of the above-mentioned problems and has an aim to provide a film formation apparatus capable of forming an EL layer with a high throughput, a high density, and a high purity. An other aim of the invention is to provide a film formation method using the film formation apparatus of the invention.
Additionally, another aim of the invention is to provide a cleaning method for removing deposition materials adhering to jigs installed in the inside of the film formation apparatus of the invention and the inner wall of the film formation apparatus without exposing them to the atmospheric air and to provide a film formation apparatus provided with the mechanism for carrying out the cleaning method. Incidentally, in the specification, the jigs installed in the inside of the foregoing film formation apparatus include a substrate holder, a mask holder, a deposition preventing shield and a deposition mask.